The present invention relates to an ultrasonic diagnostic apparatus for transmitting an ultrasonic wave to a living body and receiving a wave reflected by the living body to produce a tomographic image from the reflected wave.
An ultrasonic diagnostic apparatus has been conventionally used for medical diagnosis for the purpose of producing organic information of a living body or a patient. This ultrasonic diagnostic apparatus transmits an ultrasonic pulse into an organ of the patient through an ultrasonic probe and receives the reflected wave from a boundary surface between tissues different in acoustic impedance through the ultrasonic probe to convert the reflected wave into an electric signal. Further, the ultrasonic diagnostic apparatus displays an ultrasonic tomographic image on a monitor on the basis of the electric signal.
In such a ultrasonic diagnostic apparatus, the depth from the organic surface in which an ultrasonic tomographic image can be produced, namely, a limit of visible depth becomes shallower the higher frequency of ultrasonic wave is used for diagnosis because an ultrasonic wave is heavily absorbed by the organ in proportional to the frequency of the ultrasonic wave. However, it is desirable to use a high frequency wave in order to produce an ultrasonic tomographic image of a high resolution.
In transmission of an ultrasonic wave, it is desirable to increase the frequency of the ultrasonic wave to be transmitted in order to increase the resolution of a target region for diagnosis. However, even if the depth set to be displayed on the monitor, namely, the depth of field of view is set deep, the limit of visible depth is constant because the frequency of the ultrasonic wave to be transmitted is constant.
Conventionally, the ultrasonic diagnostic apparatus as described in Japanese Patent Public Disclosure No. 6-54850 is well known. The construction of this apparatus is shown in FIG. 5. In FIG. 5, a system controller 112 controls a drive frequency for an ultrasonic probe 115 according to a focus position, a color display area or a Doppler signal detection position. According to this apparatus, the frequency of the ultrasonic wave is changed according to the focus position, the color display area or the Doppler signal detection position.
However, the conventional apparatus as set forth above has disadvantages that even if the depth of field of view is set deep in order to display the diagnostic target region, the visual depth limit does not change because the transmitting frequency does not change and as a result, it is difficult to produce organic information on the area surrounding the diagnostic target region.
Further, the conventional apparatus has disadvantages that even if the depth of field of view is set shallow in order to display the diagnostic target region, the resolution of the diagnostic target region does not change because the transmitting frequency does not change and as a result, it is difficult to produce an image of high resolution.
Further, the conventional apparatus has disadvantages that even if the enlargingly displayed area of field of view is set deep in order to enlargingly display the diagnostic target region, the visible depth limit does not change because the transmitting frequency does not change and as a result, it is difficult to produce organic information on the area surrounding the enlargingly displayed area of field of view.
Further, the conventional apparatus has disadvantages that even if the enlargingly displayed area of field of view is set shallow in order to enlargingly display the diagnostic target region, the resolution of the enlargingly displayed area of field of view does not change because the transmitting frequency does not change and as a result, it is difficult to produce an image of high resolution.
Further, the conventional apparatus has disadvantages that even if the field of view is changed, the transmitting frequency cannot be changed without changing the focus position, the color display area or the Doppler signal detection position in the field of view.
It is an object of the present invention to solve the problem set forth above in the prior art and to provide an improved ultrasonic diagnostic apparatus capable of automatically changing an ultrasonic wave to be transmitted according to the field of view.
The ultrasonic diagnostic apparatus of the present invention comprises ultrasonic transmitting/receiving means for transmitting an ultrasonic wave to a living body and receiving a wave reflected from the living body to convert the reflected wave into an electric signal, control means for controlling the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means according to a field of view, and display means for displaying a diagnostic image on the basis of the electric signal from the ultrasonic transmitting/receiving means. In this arrangement, the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means can be automatically changed according to the field of view.
In the ultrasonic diagnostic apparatus of the present invention, the control means may be arranged to control the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means according to the depth of field of view. In this arrangement, the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means can be automatically changed according to the depth of field of view.
In the ultrasonic diagnostic apparatus of the present invention, the control means may be arranged to control the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means according to the position of the enlargingly displayed area of field of view. In this arrangement, the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means can be automatically changed according to the position of the enlargingly displayed area of field of view.
In the ultrasonic diagnostic apparatus of the present invention, in addition to an arrangement comprising ultrasonic transmitting/receiving means for transmitting an ultrasonic wave to a living body and receiving a wave reflected from the living body to convert the reflected wave into an electric signal, control means for controlling the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means according to a field of view, and display means for displaying a diagnostic image on the basis of the electric signal from the ultrasonic transmitting/receiving means, the ultrasonic diagnostic apparatus may be arranged to further include a rewritable retention table for diagnostic condition data. In the arrangement, a user can change easily such a setting that the frequency of the ultrasonic wave to be transmitted by the ultrasonic transmitting/receiving means can be automatically changed according to the field of view.